1. Field of the Invention
The present invention relates in general to an image forming apparatus, and more particularly to an image forming apparatus with a top-mounted photosensitive drum and being capable of reducing wear of the photosensitive drum.
2. Related Art
In a conventional printer, the photosensitive drum, which is mounted at the side of or under the developing unit, constantly withstands a weight or a lateral locking force of the developing unit, especially when the developing unit contains a toner supplier. Therefore, the pressing contact between the photosensitive drum and the developing roller of the developing unit produces excessive friction therebetween. Consequently, the increase in friction causes rapid wear of the photosensitive film of the photosensitive drum and shortens the life of the photosensitive drum.
The toners inside the toner supplier gradually decrease as the amount of usage increases, and therefore, the toner supplier becomes lighter in weight. To maintain the contact between the developing roller and the photosensitive drum even when the least amount of the toners remains in the toner supplier, the developing roller is usually designed to press against the photosensitive drum at a high level of pressure in the case of a full tank of toners. However such high level of pressure on the photosensitive drum only accelerates a deterioration of the photosensitive drum and consequent impact on images is liable to occur.
In addition, in the situation where the developing unit is mounted in a case with a lock device pushing the developing unit towards the photosensitive drum, the increase in the pressure applied on the photosensitive drum causes the expedited deterioration as well.